In the past, various different types of electrical circuits were utilized for controlling the operation of an automotive type air conditioning system. For instance, some of the past electrical circuits had a control device with a snap-acting switch operable therein in response to a preselected low fluid pressure of refrigerant at a low fluid pressure or suction side of a compressor in the air conditioning system to selectively energize a coil of a clutch device thereby to couple it in driving relation with a refrigerant compressor in the system. When so driven, the compressor was operable to compress the refrigerant so as to vaporize it at a high fluid pressure and temperature, and such vaporized refrigerant was circulated in the system to a condenser. Upon passing through the condenser, the vaporized refrigerant was, of course, cooled and condensed back to its liquid state at a high fluid pressure, and from the condenser, the liquid refrigerant was orificed or passed through an expansion valve or tube. Of course, upon the orificing or expansion of the cool high fluid pressure liquid refrigerant through the expansion valve, the refrigerant experiences a pressure drop and again changes state to a low pressure vapor, and in this cooler low fluid pressure vaporized state, the refrigerant passes through an evaporator and back to the suction side of the compressor. Thus, when the fluid pressure of the refrigerant at the suction side of the compressor attains a preselected high value, the snap-acting switch of the control device is operable in response thereto to effect the deenergization of the clutch device coil thereby to uncouple the clutch device from its driving relation with the compressor interrupting its operation in the system.
One of the disadvantageous or undesirable features of this past electrical circuit discussed above was believed to be that the snap-acting switch operable in such circuit created an objectionable noise or clicking sound which is audible in the passenger compartment of the vehicle in which the air conditioning system was employed. Another disadvantageous or undesirable feature of the electrical circuit discussed above is believed to be that undesirable chatter of the clutch device may have been engendered which, of course, might result in undue wear of the clutch device and perhaps premature failure thereof.
In other of the past electrical circuits for controlling the operation of an automotive type air conditioning system, such as illustrated in U.S. Pat. No. 4,256,973 for instance, a pair of creep type switches were utilized in conjunction with solid state circuitry to control the operation of the refrigerant compressor in the system; however, it is believed that a disadvantageous or undesirable feature of this patented circuit involved the complexity thereof as well as the cost of the solid state circuitry.